Alcoholic liver disease (ALD) progresses from a normal liver, to alcoholic steatohepatitis, fibrosis and hepatocellular carcinoma (HCC). Despite of intensive studies, the pathogenesis of ALD is poorly understood due to the lack of animal models which mimic the stages of ALD progression. Furthermore, the role of IL-17 in ALD has not been evaluated. We have recently demonstrated that IL-17 signaling plays a critical role in development of liver fibrosis and cancer. Based on our preliminary data, IL-17 signaling also required for ALD, and mice devoid of IL-17 signaling develop less steatohepatitis and fibrosis. Here we propose to further explore the role of IL-17 in ALD, using an improved model of ALD in mice, which was developed as a result of a collaborative effort of Drs. Karin, Gao, Tsukamoto and Kisseleva. This model most closely reproduces the stages of ALD and reflects physiological ALD progression from steatohepatitis to alcohol-induced liver fibrosis and HCC in patients. Our central hypothesis is that IL-17 exacerbates progression of ALD from steatohepatitis to fibrosis and HCC. The goal of the study is to determine if the strategy of blocking IL-17 will have a therapeutic effect on ALD. The role of IL-17 signaling in ALD, and pathways of IL-17 regulation will be tested in this study using IL-17-/-, IL-17RA-/-, and several cell-specific knockout mice to determine the role of IL- 17 signaling 1) chronic-binge model that mimics early stages of steatohepatitis (AIM 1), 2) intragastric ethanol feeding model that mimics alcoholic steatohepatitis and fibrosis (AIM 2), and 3) diethylnitrosamine (DEN)+alcohol model that mimics alcoholic liver cancer (AIM 3). Specifically, these models will allow us to dissect specific IL-17 functions at different stages of ALD. Thus, for each model, 1) development of alcohol- induced liver injury will be determined by measuring alcohol-metabolizing enzymes dehydrogenase (ADH), cytochrome, P4502E1 (CYP2E1), expression of adipogenic genes (PPAR?, PPAR?, CEBP1), lipid peroxidation, ROS production. 2) The role of IL-17 in recruitment of inflammatory cells, Kupffer cells/macrophage activation will be determined. 3) The cellular sources of IL-17 will be identified. 4) The IL-17 target cells that critically mediate ALD progression will be determined, specific cell types will be isolated and ex vivo analyzed. 5) We will generate conditional IL-17RA-/- knockout mice in Kupffer cells, hepatocytes and Hepatic Stellate Cells (HSCs) to study their contribution to ALD. 6) The global cytokine expression profile will determined for each type of knockout mice. 7) The regulatory role of IL-23, IL-25 and IL-27 cytokines in IL-17 by Th17 cells (or other IL-17 producing cells) will be determined. These unique genetic studies will provide an insight into usefulness of IL-17 inhibitors as a novel approach to treat ALD in patients.